Optical system for x-ray screen image intensifiers



ZQ L/ 'y w 4 2 I 9'57 March 10, R L. LQNG|N| OPTICAL SYSTEM FOR mmSCREEN IMAGE INTENSIF'IEIRS y 3 go Filed July 14, 1948 WITNESSES:INVENTOR' Ezchard L. Lonyznz. v BY 7 ATTOR A Q n 1 3 c Q Patented Mar.10, 195

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IMAGE 1N TENSIFIERS' Richard L. Longinl, Pittsburgh, Pa., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application July 14, 1948, Serial No. 38,586

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My invention relates to optical systems and, in particular, relates toan improved type of optical system for viewing images produced onscreens such as the fluorescent screens employed in X-ray apparatus.

For many purposes'in which images are produced by X-rays and the like,it is desirable to be able to view the image instantly on a fluorescentscreen. Fo example, in medical work, it would be desirable for manydiagnostic purposes to be able to view on a fluorescent screen an imagof the internal organs of a patient during their normal activities.However, it is well known that where the X-ray radiation is kept withinlimits which the patient may safely tolerate, the image produced on afluorescent screen is undesirably faint and cannot be viewed by thediagnosti'cian' in" *aetair"evenarter remainmg in a darkened room for aperiod of the order of half an hour to accustom his eyes to the lowluminous intensities on the screen.

An arrangement in which the image on the fluorescent screen of such anX-ray equipment can be reproduced instantaneously with an enormousincrease of intensity is described in Longini and Hunter Patent2,555,545 issued June 5, 1951, for an Imag Intensifier, filed August 28,1947, and assigned to the assignee of the present application whichclaims certain subject matter herein disclosed. Briefly, theabove-mentioned image intensifier produces on a photo-electric screenclosely adjacent the fluorescent screen an electron image which is areplica of the luminous image, and produces a second luminous image ofgreatly enhanced intensity but smaller dimensions on a secondfluorescent screen which is viewed by the diagnostician through asuitable magnifying optical system. The present invention constitutes animprovement on the optical system described in the above-mentionedLongini and Hunter application.

The photo-electric and fluorescent screens of the above-mentionedapplication are disposed in a light-optical system which will erect theimage. This latter requirement lengthens the distance between thediagnostician and the patient.

One object of my invention is, accordingly, to provide a novel type ofoptical system in which the diagnostician is able to take a positionsuitably close to the patient during observation.

Another object of my invention is to provide a novel type of opticalsystem which at once reduces the separation between the diagnosticianand the patient and produces an erect image for observation. 7

Another object of my invention is to provide an improved type of imageintensifier system for viewing images on screens produced by radiantenergy.

Still another object of my invention is to provide an improved"arrangement "for observing X-ray patterns of objects opaque to visibleradiation.

Still another object of my invention is to provide an improved apparatusfor X-radiation of patients for medical purposes.

A still further object of my invention is to provide an improved opticalsystem for viewing images on fluorescent screens.

Other objects of my invention .will become apparent upon reading thefollowing description, taken in connection with the drawing, in which:

Figure 1 is a general plan view of an X-ray apparatus being employed bya diagnostician for observation of a patient, which apparatus embodiesthe principles of my invention;

Fig. 2 is a perspective view of a novel type of reflecting prism forminga part of the optical system embodied in my invention;

a highly evaculated electron tube, and since the which makes itinconvenient for him to aid in properly positioning and manipulating the1atter to obtain theview which he desires. Furthermore. the electronlenses employed in the vacuum tube produce an inverted or reversed imageon the fluorescent screen which the diagnostician is to view, and it isnecessary to provide Fig. 3 is a sectional view in the plane III- -IIIReferring in detail to Fig. Lian X-ray tube of conventional type is usedto irradiate a patient or other object 2 and throw an X-ray imagethereof on a fluorescent screen 3 in a manner too wellknown in theradiographic art to require further description. The fluorescent screen3 forms an end wall in a high-vacuum tube 4 of the general typedescribed in the Longini and Hunter patent already referred to. Thevacuum tube 4 may be of cylindrical form having one transparent end wallon which the fluorescent screen 3 is positioned and having a second endwall 5 of glass supporting a screen comprising finely divlded particlesof an electron-phosphor, such as zinc cadmium sulphide, also describedin the first of these planes and the dot above-mentioned Longini andHunter applicais positioned a photo-emissive layer which may beseparated from the fluorescent screen 3 by a thin layer of glass or thelike. The tube 4 is provided with an electrostatic field electronoptieal system (not shown).

The arrangement so far described is disclosed in more detail in theabove-mentioned Longinl and Hunter patent and operates in the followingway: The X-ray image of the patient produced 'phor screen 5. Theelectrostatic field above mentioned is arranged to converge the paths ofthe electrons within the tube 4 and to produce on the screen 5 aluminousimage which is a replica of that on the screen 3, except that itis prefer- 'ably of substantially smaller diameter and is of abrightness which is of the order of 500 times that of the image on thescreen 3.

As described in the above-mentioned Longini and Hunter patent, anoptical system is arranged which projects along the line of the centralaxis of the tube 4 and permits an observer to see an 4 line -23 wouldlie in the second of these planes.

The prism likewise would consist of two other planes. one comprising thepoints 22-23-25-21 and the other comprising the points 23-24-28- 26,these planes intersecting each other in the line 26-23 and beingpositioned at right angles to each other. The intersection 23-26 isperpendicular to the intersection 21-25 and makes an angle of 45 degreeswith each of the planes 2 l-22-23-24-25 and 2l-25-28-26-2'l. The edge2l-25 would similarly make an angle of 45 degrees with each of theplanes 22-23-26-21 and 24-23-26-28. The planes so far described wouldnormally form peaks similar to those at 23 and 26 above the triangle2l-22-21 and belowtriangle 24-25-28 in Fig. 2; but for convenience insupporting the prism these peaks are ...removed .by...the .two. .planefaces so, numbered enlarged image of the visible picture on the screenscreen 5, and altogether it substantially lengthens the distance fromthe object 2 along the axis of the tube 4 to the eye of the observer.many cases is an inconvenience, inasmuch a the observer is'not withineasy reach of the object 2. In accordance with my invention, I providean improved type of optical system in which a roof-prism l I, not onlyinverts the image appearing on the screen 5, but turns the light raysemanating from it through a 90-degree angle so that they may be observedby a diagnostician positioned at one side of the axis of the tube 4 andwithin easy arms len th of the irradiated object 2.. An ancillaryoptical system l2 may, if desired, be positioned between the observerand the face of the roof-prism I I.

One meansof doing this is to be described. .This particular arrangementof elements should not be construed as limiting my idea.

Turning to Figs. 2, 3 and 4, the form of the roof-prism will bedescribed in more detail. Referring to Fig. 2, the prism, for reasonsabout to be discussed in more detail, preferablyhas faces which are notplane but spherical; but for purposes of clarity, it will first bediscussed as though it comprises plane surfaces, and the reasons andfunctions of the curvature imparted to the surfaces will then bediscussed.

The prism may be considered to comprise one plane surface containing thepoints 2 l-22-23- 24-25 which intersects another plane surface2l-25-28-26-2'I, said two planes being at right angles to each other.2l-25 would be the intersection of these planes; .and in Fig. 4, theline 23-25 wol ie in the 1 straight This in which are perpendicular tothe intersection Fig. 3 represents a section of the prism made bypassing a plane through the line 2l-25 normal to the line 26-23. Fig. 4is the section resulting from passing a plane through line 23-26 normalto the line 2 l-25.

The prism H is positioned in the optical system of Fig. 1 with the plane2l-22-23-24-25 flat against the screen 5. The surfaces 22-23- 25-2'! and24-23-26-28 may be coated with silver to make them highly reflective,and if this is done, it will be found that a ray of light starting fromthe image on the screen 5 will enter the prism at the point 3| and bereflected from the surface 24-23-26-28 along such a line as 32-33. Uponstriking the silvered surface 22- 23-26-21, it will again be reflectedalong the line 33 34 "to emerge frorrrthe *prism II in a In Fig. 3, theline direction at right angles to that at which it entered at the point3i. The optical properties of such a prism are such that light rays froman image on the screen 5 will, after traversing the prism with thesuccessive reflections above mentioned, form a reversed image of theview onthe screen 5 which is projected in a direction at right angles tothe axis of the tube 4. An observer may, accordingly, view such an imagein a direction at right angles to said axis.

While the foregoing describes the properties of a true prism with planesurfaces, such an image as has just been described would be of the samesize as that on the screen 5, and it is desirable for present purposesto considerably magnify'the dimensions of the observed image. In orderto accomplish this result, the surfaces 22-23- 26-21 and 24-23-26-28 arealtered from true planes to make them constitute concave sphericalmirrors having the radius of curvature necessary to produce the desiredmagnification of the image. The degree of curvature of sphericalreflectors required to produce the desired magnification may, of course,be calculated by well known optical laws. For most purposes, thecurvature of the two spherical surfaces should be the same anddistortion will be minimized by making it not too great. H In order tofurther magnify the observed image, the surface erably ground to fit theexternal surface ofthe electron-phosphor screen 5, and is cemented tothat end of the tube 4.

In certain instances, it will be found that the electron optical systemcomprised within the tube of the combined optical system in whichdistor-.

tion would individually exist.

- The arrangement of Fig. 1 may be provided with a suitable casing l3 ina manner well known "in *the art to exclude undesired-rl-ight -strom.the

optical system.

In Fig. 3, the point 35 is the mid-point of the intersection 23-26; theline 3538 is the intersection of section-plane III with the surface21-23-28-21, and the line 35-31 is the intersection of thatsection-plane with the surface 23--24-28--26.

In Fig. 4, 23-;25is the intersection of sectionplane IV line 2H 26 isthe intersection of that sectionplane with surface 2l-25--28-26 -21.

While I have described the foregoing arrange- 6 a spherical reflectingsurfaces substantially at right angles to eachother and having a line ofintersection forming substantially equal angles t its points ofintersection with said output screen, and optical magnifying means inthe path of light reflected fronfsald'l'eflecting surfaces.

4. An image intensifier comprising an electron optical system producinga luminous image on a screen forming a wall portion thereof and aroof-prism traversed by the light from said image comprising one surfacecontiguous to saidscreen, a second surface of spherical contoursubstantially at right angles to said screen, said prism also comprisingtwo reflecting spherical'surfaces substantially at right angles to eachother intersecting each other in a line which makes substantially equalangles at its intersection with each of the first two surfacesmentioned, and

,. ..optical. magnifying,means in thepath of light ith surface2i-22-23--24-25; and

ment as utilized for observation of X-ray images V any by non visibleradiations 'or otherwise.

I claim as m invention: 1. In combination with an electronicimageintensifler having an output screen on which a reflec d from saidreflecting surfaces.

5. A X-ray apparatus comprising means for formingyan X-ray image of anirradiated object on a fluorescentscreen, an electron optical imageintensifier comprising a substantially cylindrical high vacuum tubehaving its axis normal to said screen and having an output screensubstantially normal to said axisf"ai bof-prism traversed by light fromsaid output screen comprising two surfaces substantially at right anglesot each other. one said surface being positioned adjacent to said outputscreen. and the other said surface being spherical; said prism alsocomprising two other spherical-reflecting surfaces substantially atright angles to each other and having a line of intersection formingequal angles with each of the two surfaces first mentioned.

6. A roof-prism comprising two surfaces sub- "stantiallyatmightangles-"to :each other, one of luminous image appears, aroof-prism traversed 1 by the light from said, luminous image forpermitting said image to be viewed from-a position at one side oftheaxis of said image intensifier, said roof-prism having two reflectingsurfaces, and a third surface of spherical contour traversed by thelight reflected from one of said reflecting surfaces.

2. An X-ray apparatus comprising means for forming an X-ray image of anirradiated object on a fluorescent screen, an electron optical imageintensifier comprising a substantially cylindrical high vacuum tubehaving its axis normal to said sgejefinpand having an output screensubstantially no al to said axis, a roof-prism traversed by light fromsaid outputscreen comprising two surfaces substantially at right anglesto each other. one said surface being positioned adjacent to saidoultfput screen, said prism also comprising two sp erica reflectingsurfaces substantially at right angles to each other and having a lineof intersection forming equal angles with each of the two surfaces firstmentioned.

3. An X-ray apparatus comprising means for forming an X-ray image of anirradiated object on a fluorescent sgeen, an electron optical imageintensifier comprising a substantially cylindrical higfiVaEuum tubehaving its axis normal to said screen and having an oi t put scr eensubstantially normal to said axis, a roof-prism traversed by light fromsaid output screen comprising two surfaces substantially at right anglesto each other, .one surface being positioned adjacent to said l putscreen, said prismalso comprising two said surfaces constituting theentrance face of said roof-prism being optically cemented to an electrgiphosphor screenand the other of said surfaces constituting the exit faceof said roofprism being curved, said prism comprising also two othersurfaces substantially at right angles to each other, saidother-surfaces being light reflecting and each having slight sphericalcurvature with the concave surfaces toward each other,

and having a curve of intersection forming substantially equal angleswith the normal to said first surface and with the optical axis of saidsecond surface whereby said reflecting surfaces form the roof of saidroof -prism.

7. An optical transmission element comprising a prism having a phosphorscreen optically continuous with one of its surfaces which constitutesthe entrance face of said-prism. a second surface of curved form havingits optical axis substantially parallel to said screen and constitutingthe exit face of said prism, said prism also comprising two sphericalsurfaces having central axes substantially at right angles to each otherand having a line of intersection forming an angle of substantially 45with said screen, said two' an electron optical image intensifiercomprising means for projecting into incidence with an output sgeenpositioned in the path of said beam an electron image which is areversed replica to small scale of that on said fluorescentscreen.

' a reflector for said output screen comprising two surfacessubstantially at right angles to each '-'section with saidoutputscreen'toweilect the' light other and having a line ofintersection forming substantially a 45 angle at its point ofintertherefrom in a beam substantially parallel to said output screenand withinless than arms length. distance of said object, and opticalrnag-z nifying means in the path of the last mentioned beam,

RICHARD L. LONGINI.

Number Number f s REFERENCES CITED The following references are ofrecord in the file of this patent:

UNITED STATES PATENTS Name Date Moller Mar. 14, 1911 Roach Feb. 10, 1925Wappler ---a Sept. 22, 1936 Ogloblinsky Sept. 14, 1937 Coolidge May 16,1939 Loebell July 16, 1940 Gardner July 7, 1942 Bertele June 29, 1943Konigsberg Dec. 28, 1943 Kallmann Mar. 14, 1944 -=Young 'Apr. 18, 1944Lawlor Nov. 28, 1944 FOREIGN PATENTS 1 Country Date Great Britain July31, 1919 France NOV. 10, 1942

